Electrically-programmable microelectromechanical (MEM) diffraction gratings, which have been developed in recent years, can be used for processing light beams for applications including spectroscopy, remote sensing, optical information processing and the routing of optical signals for telecommunications (see e.g. U.S. Pat. Nos. 5,757,536; 5,905,571; and 6,329,738). These MEM diffraction gratings, also termed polychromators, are based on a series of moveable elongate grating elements formed on a substrate, with the grating elements being moveable singly or in sets in a direction normal to the substrate for programming a particular grating pattern within the device to control and tailor the reflection of an incident light beam. The grating elements can be up to one centimeter in length, with a width that is generally about 10–20 μm, and with a vertical range of movement that is a fraction of the wavelength of the incident light for which the device has been designed.
Due to atmospheric transmission considerations, the 8–12 μm wavelength range is optimal for infrared chemical sensing using correlation spectroscopy. In addition, this 8–12 μm spectral band often contains the chemical “fingerprint” bands that help to uniquely determine chemical species of interest. However, the optimal operation of an electrically-programmable MEM diffraction grating in this wavelength range requires that the individual grating elements have a relatively large range of vertical movement equal to one-half wavelength of the incident light (i.e. 4–6 μm vertical movement). This relatively large range of vertical movement is difficult, if not impossible, to achieve with the electrically-programmable MEM diffraction gratings of the prior art.
The present invention represents an improvemment over the prior art by providing a MEM apparatus for redirecting incident light that can be used to form an electrically-programmable diffraction grating or micromirror array which can provide an increased range of vertical movement for controlling a phase shift or tilt angle of the reflected light. The increased range of movement is provided by two electrostatic actuators stacked one upon the other, with the two or more electrostatic actuators being operable simultaneously or sequentially.
The present invention also allows an electrically-programmable diffraction grating elements to be formed from a series of unconnected segments arranged end-to-end to accommodate the residual stress associated with a particular MEM fabrication process, and thereby prevent any surface distortion or buckling which might otherwise occur by forming continuous centimeter-long diffraction grating elements.
These and other advantages of the present invention will become evident to those skilled in the art.